Dual-modality imaging systems that use a combination of full-field digital mammography and automated breast ultrasound imaging in a single device are known. These devices combine the benefits of both imaging techniques to obtain more effective and accurate diagnosis of carcinoma or other abnormalities in particularly breast tissue.
The applicant's international patent applications number WO2011/153555 entitled “DUAL-MODALITY SCANNING SYSTEM FOR DETECTING BREAST CANCER” and number WO/2014/097231 entitled “DUAL-MODALITY MAMMOGRAPHY”, disclose such dual-modality scanning apparatus that incorporates both X-ray and ultrasound technologies.
WO2011/153555 and WO/2014/097231 are incorporated herein, in their entirety, by reference.
As described in more detail in WO2011/153555 and WO/2014/097231, in use, biological tissue to be scanned, typically a breast, is compressed between a first surface, also referred to as a scanning surface or compression plate, and a compression paddle which is mechanically lowered onto the breast. In one embodiment, the scanning surface forms part of a housing within which a dual modality scanning element comprising an X-ray detector and ultrasonic transducer is mounted on a drive below the scanning surface. Such a dual modality scanning element enables simultaneous acquisition of X-ray and ultrasound images of the breast tissue compressed between the scanning surface and the compression paddle. The scanning element moves on the drive in a plane parallel to the scanning surface for imaging of the tissue through the scanning surface and parallel to a plane defined by the transverse movement of the X-ray source. A linear drive means is provided that moves the scanning element along rails.
In one embodiment the housing is hermetically sealed and is filled with a non-conductive fluid with an acoustic impedance resembling that of the tissue, completely immersing the scanning assembly and drive in the fluid. The purpose of the fluid is to provide ultrasonic coupling between the scanning assembly and the tissue in use. A hermetic seal ensures that the fluid is kept at a constant volume during use. Due to the sealed and filled nature of the housing, the housing is substantially less compressible than it would have been had it not been for the presence of the fluid. The incompressibility of the housing allows both the X-ray detector and ultrasound transducer to move and scan very close to the underside of the scanning surface and, accordingly, the breast tissue, which minimises X-ray signal attenuation that may be caused by the fluid and the geometric magnification due to the finite X-ray focal spot.
The hermetically sealed housing must be devoid of water or air, as it will interfere with the acoustic impedance of the fluid. During manufacturing of the scanning assembly, the filled housing is drained and dried to remove all water and air.
The scanning surface of the housing may be made from polymethylpentene, a thermoplastic material better known commercially by its trade name “TPX®”. TPX® is a lightweight polyolefin with exceptional acoustical and electrical properties. TPX® has low moisture absorption and excellent chemical resistance. It is often used for applications requiring low distortion of sound waves including sonar covers, speaker cones, and ultrasonic transducer heads.
Previous approaches used to secure a TPX® plate which forms the scanning surface to a body of a housing include the use of a stitched bond or an adhesive bond. In the latter approach, a special adhesive is used to bond the TPX® plate to the housing. After bonding, more ductile epoxy is used to waterproof the bond. However, TPX® has an unusually low surface tension (24 mN/m) and the epoxy does not adhere to it adequately. In fact, TPX® exhibits excellent peel ability and is often used as a release material at the time of curing thermosetting resins or the like. For this reason, the application of epoxy to the TPX® scanning surface is a cumbersome step in the manufacturing of a hermetically sealed housing incorporating a TPX® scanning surface and may not provide an adequate seal.
The body of the housing, which may have an edge of less than 1 mm thick, needs to be made from a suitably stiff material capable of supporting a compression load of approximately 200 N. The housing is therefore preferably, but not exclusively, made from carbon fibre-reinforced polymers (CFRP). Such materials are easily mouldable into the required shape. To manufacture the entire housing from TPX® is not feasible as the material is not stiff enough.
There is accordingly a need for a method of securing TPX® to a body, preferably made of CFRP in a way that provides adequate sealing characteristics.
In the remainder of this specification the term “scanning plate” should be construed to mean a generally planar piece of material used in a housing of a scanning assembly as described above, which forms the scanning surface through which X-ray and ultrasound imaging of tissue supported on the scanning plate is conducted.
The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.